Thrust ball-bearing

ABSTRACT

A thrust ball-bearing in which a good lubrication is maintained for a long period of time and having a long service life. The bearing comprises a plurality of balls having a uniform diameter, a retainer which retains the balls, and two plates situated at either side of the retainer and rotatable relative to each other via the balls. The retainer has a thickness less than the diameter of the ball. A plurality of holes that retain each ball is provided on the retainer and a groove having a rectangular cross section is formed in a portion between two adjacent holes. An amount of grease applied to the ball is collected inside the groove and provided to the ball located on the downstream side of flowing grease without moving outwardly of the groove even if a centrifugal force generated by a rotation of the bearing is exerted.

BACKGROUND OF THE INVENTION

The present invention generally relates to a thrust ball-bearing, andmore particularly to a thrust ball-bearing in which a plurality of ballsare held in predetermined positions by a retainer situated between twoplates.

A description will be given of an example of a conventional thrustball-bearing with reference to FIG. 1 and FIG. 2. FIG. 1 is an enlargedcross sectional view of a disk driving motor in a conventional FDD(Floppy Disk Drive) apparatus, and FIG. 2 is an exploded view of abearing portion of the disk driving motor shown in FIG. 1.

A spindle shaft holder 6 is fixed on a chassis 1 and a plurality ofcoils 4 radially surround the shaft holder 6 on the chassis 1. A spindleshaft 2 is fixed, by press fitting, to a turn-table 3 that rotates witha disk loaded thereon. A magnet 5 is provided on an inner surface of theturn-table 3 in a position such that the magnet 5 faces the coils 4.Additionally, one end of the spindle shaft 2 is inserted into thespindle shaft holder 6 and thus the turn-table 3 is rotatably supportedon the chassis 1.

A thrust force applied in an axial direction of the spindle shaft 2 ofthe turn-table 3 is carried by a ball bearing 11 which comprises plates7 and 10, a retainer 8 and a plurality of balls 9. Each of the balls 9are rotatably retained by being situated inside equally spaced holesformed on the annular retainer 8. The retainer 8 is sandwiched betweenthe two annular plates 7 and 10 from the upper side and the bottom side.Portions of each ball 9 protrude from the upper surface and the bottomsurface of the retainer 8 such that the plates 7 and 10 make contactwith the balls 9; thus the plates 7 and 10 are rotatable relative toeach other via the balls 9.

In such a ball bearing structure, it is usual to apply an amount ofgrease on a surface of the balls 9 at assembly time so that frictionbetween the balls and plates is reduced and the bearing can maintain asmooth rotation.

However, since the grease applied to the ball rotates together with theball, the grease is scooped by an edge of the hole that retains eachball and the grease is collected in portions between the retainer 8 andthe plates 7 and 10. A centrifugal force is exerted on the grease, whichforce is generated by a rotation of the bearing. Since the greasegradually moves outwardly from a portion where the ball 9 makes contactwith the plates 7 and 10, the lubrication of the ball is reduced.

Ball-bearings such as above mentioned are generally adopted for use inhome appliances to which home appliances periodical application ofgrease is not provided as in the case of industrially used appliances.Therefore, when an amount of grease decreases, from the surface of theball 9, after a considerable time of use, friction between the ball 9and the plates 7 and 10 increases.

As mentioned above, when the lubrication of the ball is decreased, wearof the balls and plates is increased and thus there is a problem in thata life of the ball bearing becomes short.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a novel andimproved thrust ball-bearing in which the above mentioned disadvantagesare eliminated.

A more specific object of the present invention is to provide a thrustball-bearing that has a long service life obtained by a long lubricationtime due to an amount of grease being kept inside the bearing.

In order to achieve the above mentioned objects, a thrust ball-bearingaccording to the present invention comprises:

a plurality of balls having a uniform diameter;

an annular retainer, having a thickness less than a diameter of theballs, being provided with circumferentially arranged holes, each of theholes receiving and rotatably retaining therein one each of the balls,and being provided with a plurality of recesses, each connectingadjacent holes and formed on portion between any two adjacent holes on asurface of the retainer, each of the recesses having an outer side wallnearly perpendicular to a radial direction of the retainer; and

two annular plates situated one at either side of the retainer so thatthe plates sandwich the balls in order to perform a relative rotationalmovement.

According to the present invention, the edge formed by the hole and therecess scoops the grease, and the scooped greased is collected insidethe recess. The grease inside the recess is prevented, by means of theouter side wall of the recess, from outward movement caused bycentrifugal force. Thus the grease remains inside the recess and isapplied to the ball again; this results in a long service life of thebearing due to a long lubrication time by the grease.

Other objects, features, and advantages according to the presentinvention will become more apparent from the following detaileddescription when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross sectional view of a driving motor of aconventional FDD apparatus;

FIG. 2 is an exploded view of the thrust ball-bearing shown in FIG. 1;

FIG. 3 is an exploded view of a first embodiment of a thrustball-bearing according to the present invention;

FIGS. 4 are views of an essential part of the embodiment shown in FIG.3; FIG. 4A shows a plan view; and FIG. 4B shows a partially cutaway sideview;

FIG. 5 is an exploded view of a second embodiment of a thrustball-bearing according to the present invention; and

FIGS. 6 are views of an essential part of the embodiment shown in FIG.5; FIG. 6A shows a plan view; and FIG. 6B shows a cross sectional view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given of a first embodiment of a thrustball-bearing according to the present invention with reference to FIGS.3, 4A and 4B. FIG. 3 is an exploded view of a first embodiment of athrust ball-bearing 13 according to the present invention, and FIG. 4Ais a plan view of a retainer, which is an essential part of the firstembodiment, and FIG. 4B is a partially cutaway side view of theretainer. It should be noted that the thrust ball-bearing 13 of thisembodiment is, similarly to the above mentioned conventional thrustball-bearing, used in a spindle motor of an FDD apparatus.

As shown in FIG. 3, the thrust ball-bearing 13 of this embodimentcomprises a plurality of balls 9, for example made of steel, a retainer12, and two plates 7 and 10. The retainer 12 formed in an annularplate-like shape is provided with twelve circumferentially arranged andequally spaced spherical ball retaining holes 12a. An arc-shaped groove12b is provided in each space between adjacent holes 12a, and each endof the each of the grooves 12b is connected to respective holes 12a. Thegrooves 12b have a width smaller than a diameter of the hole 12a, andthe groove's cross section has a rectangular shape, so that an outerside wall of the grooves 12b lies nearly perpendicular to the radialdirection of the retainer 12. Each groove 12b is formed along acircumference of the retainer including a centerpoint of each hole 12a.

The thrust ball-bearing 13 of this embodiment comprises the retainer 12,in which a ball 9 is respectively provided in each hole 12a, and theplates 7 and 10 made, for example, of steel, the plate 7 and 10 beingrespectively located on either sides of the retainer 12. Each ball 9 isrotatable in a state where the ball 9 is situated in the hole 12a of theretainer 12. Since a thickness of the retainer is slightly less than adiameter of the ball 9, portions of the ball 9 protrude from the upperand bottom surfaces of the retainer 12. Accordingly, the plate 7 and theplate 10 can rotate relative to each other while a thrust force, whichexerts a force in a direction perpendicular to the plane of theretainer, is applied thereon.

When assembling the ball bearing 13, an amount of grease, which is usedfor lubrication, is applied to a surface of each ball 9 and inside eachgroove 12b.

When the plate 10 rotates with respect to the plate 7 in either ofdirections indicated by arrows in FIG. 3, each ball 9 tends to move in adirection tangential to a rotational direction of the plate 10. However,since a radial movement of the balls 9 is restricted by the retainer 12,each ball 9 performs a rotational movement corresponding to that of theplate 10. The retainer 12 rotates in the same direction as the balls 9rotate. The rotational speed of the retainer 12 is approximately half ofthat of the plate 10.

During the rotation of the retainer 12, the grease provided inside thegrooves 12b experiences a centrifugal force and tends to move outwardly.However, the movement of the grease inside the grooves 12b is preventedby an outer side wall of the grooves 12b, and thus the grease cannoteasily go out of the grooves 12b. Since the grease rotates as theretainer rotates, a force due to inertia is exerted on the grease, andthe grease tends to move in a direction opposite to the rotationaldirection of the retainer 12. By this inertia of the grease, the greaseslowly moves toward the ball 9 located in the downstream side of thegrease flow, and the grease finally comes in contact with a surface ofthe ball 9 situated on the downstream side thereof.

As mentioned above, the grease inside the grooves 12b is applied to theballs 9 without the grease moving out from the grooves 12b due to acentrifugal force generated by a rotation of the ball bearing.Therefore, the ball bearing 13 of this embodiment is able to have a longlubrication time, thus obtaining a long service life of the bearing.

Next, a description will be given, with reference to FIGS. 5, 6A and 6B,of a second embodiment of a thrust ball-bearing according to the presentinvention. FIG. 5 is an exploded view of a second embodiment of a thrustball-bearing 15 according to the present invention, FIG. 6A is a planview of a retainer, which is an essential part of the second embodiment,and FIG. 6B is a cross sectional view of the retainer. It should benoted that the thrust ball-bearing 15 of this embodiment is, similarlyto the above mentioned conventional thrust ball-bearing, used in aspindle motor of an FDD apparatus.

Similarly to the first embodiment, the retainer 14 formed in an annularplate-like shape is provided with twelve circumferentially arranged andequally spaced spherical ball retaining holes 14a. An arc-shaped groove14b is provided in each space between adjacent holes 14a and each end ofeach of the grooves 14b is connected to respective holes 14a. However,unlike in the first embodiment, one half of each of the grooves 14b isprovided on one surface (top surface) of the retainer 14 and the otherhalf of each of the grooves 14b is provided on the opposite surface(bottom surface) of the retainer 14. The grooves 14b are alternatelyprovided on the surfaces of the retainer 14, that is, only one of eithertop surface or bottom surface grooves 14b is provided between adjacentholes 14a on the retainer 14.

A width of each groove 14b on one end gradually increases toward theoutside of a radial direction, and the width of each groove 14b at anedge connected to the respective hole 14a reaches to the outermost pointof the hole 14a, as shown in FIG. 6A.

Wide ends of grooves 14b located on the same surface of the retainer 14are directed along the same direction along the circumference of theretainer 14. The wide ends of each groove 14a on the opposite surface ofthe retainer 14 are directed all in the same direction opposite to thatof the other surface mentioned above.

When the plate 10 rotates in a direction indicated by an arrow A of FIG.5, the balls 9 rotate in a direction indicated by an arrow B of FIG. 5;causing a rotation of the retainer 14 in a direction indicated by anarrow C of FIG. 5. The rotational speed of the retainer 14 isapproximately half of that of the plate 10.

The grease, adhered to a surface of each of the balls 9, rotates withthe balls 9 and is scooped by edges 14c of the widened sides of thegrooves 14b. Accordingly, the scooped grease is collected inside thegrooves 14b. Similarly to the first embodiment, the grease inside thegrooves 14b moves towards the downstream side and lubricates the balls9.

As mentioned above, in this embodiment, the grease is collected from awide area of a surface of the ball 9. The grease can be collected onboth sides of the retainer 14 as the grooves 14b are provided on bothsurfaces of the retainer 14.

Accordingly, the grease inside the groove 14b is maintained inside thegrooves 14b for a long period of time and is applied to the balls 9 forlubrication without moving out of the grooves 14b due to a centrifugalforce generated by a rotation of the ball bearing 15. Therefore, animprovement is obtained in the service life of the bearing 15.

Although the thrust ball-bearing of the first embodiment has groovesprovided only on one surface and the bearing of the second embodimenthas grooves provided alternately on the surfaces of the retainer, itshould be noted that this is due to the thickness of the retainer beingsmall, the groove may be provided at every portion between adjacentholes on both the surfaces of the retainer if the thickness issufficient to form the grooves thusly.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the

What is claimed is:
 1. A thrust ball-bearing comprising:a plurality ofballs having a uniform diameter; an annular retainer having a thicknessless than the diameter of said balls, being provided withcircumferentially arranged holes, each of said holes receiving androtatably retaining therein one of said balls, and being provided with aplurality of recesses, each recess formed on a portion of a surface ofsaid retainer between adjacent holes and connecting said adjacent holes,each of said recesses including a groove having an outer side wallnearly perpendicular to a radial direction of said retainer; and twoannular plates respectively situated at each side of said retainer sothat said plates sandwich said balls in order to perform a relativerotation. wherein said grooves are formed along a concentric circleincluding a center of each of said holes, and wherein at least one endof each of said grooves connecting to said respective hole is widenedoutwardly in the radial direction of said retainer.
 2. The thrustball-bearing as claimed in claim 1, wherein said groove is provided ateither surface of said retainer.
 3. The thrust ball-bearing as claimedin claim 2, wherein a direction of wide portions of said grooves formedon one surface is opposite to a direction of wide portions of saidgrooves formed on the other surface of said retainer.
 4. A thrustball-bearing comprising:a plurality of balls having a uniform diameter;an annular retainer having a thickness less than the diameter of saidballs, being provided with circumferentially arranged holes, each ofsaid holes receiving and rotatably retaining therein one of said balls,and being provided with a plurality of grooves, each groove formed on aportion of a surface of said retainer between adjacent holes to connectsaid adjacent holes and retaining a grease therein, each of said grooveshaving an outer side wall nearly perpendicular to a radial direction ofsaid retainer and being formed along a concentric circle including acenter of each of said holes; and two annular plates respectivelysituated at each side of said retainer so that said plates sandwich saidballs in order to perform a relative rotation, whereby the grease insideeach groove is supplied to the balls through ends of the groove duringthe rotation.
 5. The thrust ball-bearing as claimed in claim 4, whereina width of said grooves is smaller than a diameter of said holes.